Methods and systems for determining the location of an electronic device using multi-tone frequency signals

ABSTRACT

Embodiments of the present invention include a method of determining a location of a mobile device. The method comprises transmitting a signal between a plurality of known locations and receiving signal at device of unknown location such as a mobile device. The signal may include multiple tones having different frequencies and resulting in sets of residual phase differences. The location of the mobile device may be determined using the known locations and the frequency and phase differences between the transmitted tones. In one embodiment, OFDM signals may be used between an access point and mobile device, for example, to determine the location of the mobile device.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

BACKGROUND

The present invention relates to determining the location of anelectronic device, and in particular, to methods and systems fordetermining the location of an electronic device having an unknownlocation.

As electronic devices such as computers and cell phones have become moreprevalent, there is a growing desire to determine the location for suchdevices for a variety of applications. One of the most prevalentconsumer applications has been in travel. One common approach is to usea Global Positioning System (“GPS”) to determine location. GPS systemsincorporate navigation systems which help the user find their desireddestinations. Many of the systems provide navigation with visual andaudio cues that aid the user in navigating through streets and highwayswhich may be unfamiliar to the user.

However, GPS systems suffer from a variety of shortcomings GPS systemsignals are fairly weak and may not be sufficient to operate in manyindoor locations, tunnels, and urban canyons. In large cities such asSan Francisco, New York, and Chicago, there are many locations in whichGPS signals do not operate or may not provide consistent location datafor navigation. For example, if a user takes the subway around the city,the current GPS systems may not be able to determine any locationswithin the tunnels, and this may lead a user to exit the train at thewrong train station. Also, many destinations in a large metropolitancity may require a vertical coordinate as well as a longitudinal andlatitudinal coordinate. For example, a store within a mall may belocated on the top level of a building.

Thus, there is a need for improved systems and methods for determininglocation. The present invention solves these and other problems byproviding methods and systems for determining the location of anelectronic device.

SUMMARY

Embodiments of the present invention improve methods and systems fordetermining the location of an electronic device. In one embodiment, thepresent invention includes a method of determining a location of anelectronic device, the method comprising transmitting one or moresignals between a first electronic device at an unknown location andthree or more electronic devices at three or more corresponding knownlocations, wherein the one or more signals each include a plurality oftones having different frequencies, determining at least one first phasedifference between at least two tones having a first frequencydifference in the one or more signals accumulated during transmissionbetween the first electronic device and a first electronic device ofsaid three or more electronic devices, determining at least one secondphase difference between at least two tones having a second frequencydifference in the one or more signals accumulated during transmissionbetween the first electronic device and a second electronic device ofsaid three or more electronic devices, determining at least one thirdphase difference between at least two tones having a third frequencydifference in the one or more signals accumulated during transmissionbetween the first electronic device and a third electronic device ofsaid three or more electronic devices, and determining the location ofsaid first electronic device using said first, second, and third phasedifferences and said first, second, and third frequency differences.

In one embodiment, the method further comprises determining a fourthphase difference between at least two tones having a fourth frequencydifference in the one or more signals accumulated during transmissionbetween the first electronic device and a fourth electronic device offour or more electronic devices, wherein said determining the locationfurther comprises using the fourth phase difference and the fourthfrequency difference. Additional electronic devices at known locationsmay be used to determine the location of the unknown device.

In one embodiment, the devices at know locations are wireless accesspoints. In one embodiment, the device at the unknown location is amobile device such as a mobile phone, laptop computer, personal digitalassistant, or a handheld computer based system.

In one embodiment, the first, second, and third frequency differencesare the same, but the first, second, and third frequency differences maybe different.

In one embodiment, the one or more signals comprise orthogonal frequencydivision multiplexed signals.

In one embodiment, a first signal of the one or more signals comprisesfirst wireless standard and a second signal of the one or more signalscomprises a second wireless standard.

In one embodiment, a first signal of the one or more signals istransmitted from the first electronic device of said three or moreelectronic devices and received by the first electronic device at theunknown location, a second signal of the one or more signals istransmitted from the second electronic device of said three or moreelectronic devices and received by the first electronic device at theunknown location, and a third signal of the one or more signals istransmitted from the third electronic device of said three or moreelectronic devices and received by the first electronic device at theunknown location.

In one embodiment, a first signal of the one or more signals istransmitted from the first electronic device at the unknown location andreceived by the first electronic device of said three or more electronicdevices, a second signal of the one or more signals is transmitted fromthe first electronic device at the unknown location and received by thesecond electronic device of said three or more electronic devices, athird signal of the one or more signals is transmitted from the firstelectronic device at the unknown location and received by the thirdelectronic device of said three or more electronic devices.

In one embodiment, the one or more signals is one signal transmittedfrom the first electronic device at the unknown location and received byeach of said three or more electronic devices.

In one embodiment, at least one of said electronic devices comprises aplurality of antennas, and wherein the method comprises determining afirst phase difference between at least two tones received by a firstantenna of said plurality of antennas, and determining a second phasedifference between at least two tones received by a second antenna ofsaid plurality of antennas.

In one embodiment, the first electronic device at the unknown locationincludes a gyrator, wherein the method further comprises determining afirst location of said first electronic device, storing said firstlocation, generating movement vector indicating the movement of thefirst electronic device relative to first location, and adding themovement vector to the first location to determine a second location.

In one embodiment, the method further comprises estimating the distancebetween the first electronic device and at least one of said three ormore electronic devices using a transmitted power and received power ofsaid one or more signals.

In one embodiment, the method further comprises encoding the transmittedpower in at least one signal.

In one embodiment, determining the location further comprises selectinga first integer representing the difference in the integer number ofwavelengths of two tones transmitted between the first electronic deviceand said first electronic device of said three or more electronicdevices, selecting a second integer representing the difference in theinteger number of wavelengths of two tones transmitted between the firstelectronic device and said second electronic device of said three ormore electronic devices, selecting a third integer representing thedifference in the integer number of wavelengths of two tones transmittedbetween the first electronic device and said third electronic device ofsaid three or more electronic devices, and determining a first distancebetween the first electronic device and said first electronic device ofsaid three or more electronic devices, a second distance between thefirst electronic device and said second electronic device of said threeor more electronic devices, a third distance between the firstelectronic device and said third electronic device of said three or moreelectronic devices using said first, second, and third integers.

In one embodiment, the first, second, and third distances are finaldistances indicating the location of the first electronic devicerelative to three of the three or more electronic devices if the first,second, and third distances intersect at a single point.

In one embodiment, the method further comprises estimating the firstdistance between the first electronic device and said first electronicdevice of said three or more electronic devices using a transmittedpower and received power of said one or more signals and determiningsaid first integer based on said estimated distance.

In one embodiment, the method further comprises determining a pluralityof received amplitudes for the plurality of tones, processing one ormore of the received amplitudes to determine estimated distances foreach tone, weighting the estimated distances based on received amplitudevalues, and determining the location of said first electronic deviceusing said estimated distances.

In one embodiment, processing comprises normalizing a plurality ofreceived amplitudes. In one embodiment, processing comprises averaging aplurality of received amplitudes and normalizing the received amplitudesto an average amplitude value. In one embodiment, processing comprisesdetermining a highest and a lowest amplitude value of said receivedamplitudes and normalizing the received amplitudes to said highest andlowest amplitude values.

In one embodiment, the present invention includes a method ofdetermining a location of an electronic device comprising determining afirst distance between a first electronic device having an unknownlocation and a second electronic device having a known location,determining the first distance comprising generating a plurality oftones having a plurality of frequencies, modulating the tones with acarrier frequency to produce a first signal, transmitting the firstsignal between the first electronic device and the second electronicdevice, receiving the first signal, demodulating the first signal toextract the plurality of tones, extracting the phase of at least aportion of the plurality of tones, and determining phase differencesbetween tones at different frequencies, each phase difference having acorresponding frequency difference, determining a second distancebetween the first electronic device having the unknown location and athird electronic device having a known location, determining the seconddistance comprising the same method as determining the first distance,determining a third distance between the first electronic device havingthe unknown location and a fourth electronic device having a knownlocation, determining the third distance comprising the same method asdetermining the first distance, and calculating the first, second, andthird distances based on the phase differences and correspondingfrequency differences, and determining the location of said firstelectronic device based on said first, second, and third distances.

In one embodiment, the method further comprises extracting an amplitudefor each of said plurality of tones, estimating the first, second, andthird distances using said extracted amplitudes and a transmitted powervalue, selecting a first integer representing the difference in theinteger number of wavelengths of two tones transmitted between the firstelectronic device and the second electronic device, a second integerrepresenting the difference in the integer number of wavelengths of twotones transmitted between the first electronic device and the thirdelectronic device, and a third integer representing the difference inthe integer number of wavelengths of two tones transmitted between thefirst electronic device and the third electronic device, wherein theintegers are selected based on the estimated first, second, and thirddistances, and calculating the first, second, and third distances basedon the first, second, and third integers.

In one embodiment, the method further comprises determining a fourthdistance between the first electronic device having the unknown locationand a fifth electronic device having a known location, determining thefourth distance comprising the same method as determining the firstdistance, calculating the fourth distances based on the phasedifferences and corresponding frequency differences; and determining thelocation of said first electronic device based on said first, second,third, and fourth distances.

In one embodiment, the present invention includes a system that employsa multi-tone OFDM signal. A signal travels between a known locationtransmitter (e.g. a wireless access point/base-station) and a receiver(e.g. a wireless mobile device). An OFDM range engine uses the estimatedchannel frequency response vector to calculate the residual phasedifferences between frequency tone pairs and also extracts amplitudeinformation for each tone. This process is repeated with othertransmitters with known locations. All the calculated residual phasedifferences and amplitude information are then processed by a locationengine to locate the mobile device. A standard OFDM transmitter may beused for the system. The system may further include an OFDM range engineand an OFDM receiver, and possibly a location engine if the receiver isto be used for the location calculations.

Both the OFDM range engine and the location engine may be softwarealgorithms that can be implemented on a DSP. The location engine mayprocess the residual phase differences and tone amplitude information bysearching for a solution to a triangulation problem as described herein.The location engine may be a software algorithm that is running on aindependent server. Alternatively, the software may be implemented onthe OFDM transmitters or the receiver.

In some embodiments, smaller tone amplitudes may be given smallerweights in the location calculations or ignored altogether. Amplitudeinformation may also be used to detect multi-paths. For example, accesspoints that provide a direct line of sight will have fewer variations inthe amplitudes of their pilot tones and will be preferred in anytriangulation calculations in order to reduce the effects of multipath.

In embodiments using Multiple-Input and Multiple-Output (MIMO) systems,several antennas may be used to gather more data to get more accurateresults. For example, a MIMO access point acting as a transmitter canuse more than one antenna. Furthermore, these antennas may be used withthe highest performance, lowest bit error rates, and better lines ofsights.

Embodiments of the present invention may be implemented where accesspoints or base-stations are the OFDM transmitters and the mobile deviceis the receiver, or the case where the mobile device is the OFDMtransmitter and the access points/base-stations are the receivers, oryet other situations where the OFDM transmitters and receiver roles areshared. The latter may be useful in some systems where transmit andreceive frequencies are different, and switching the role of transmitterand receiver therefore provides more data samples and better averaging.Furthermore, some systems such as WLAN can operate at differentfrequencies. For example, WLAN 802.11a and 802.11g use two differentfrequencies and using both frequencies provides more data for a moreaccurate location estimate. Another way to improve the location estimateis to use several wireless standards. For example, if an access pointand a mobile device have UWB, WLAN, and cellular connectivity thenresidual phase and amplitude information may be obtained from allstandards and processed to get a more accurate location value.

After the mobile device's position is calculated it is possible tointerface the system with a navigation system that provides pathplanning and guidance. A mobile device whose position is known orcalculated can also be used as an access point to locate the position ofother mobile devices.

The proposed method can be applied to any system that uses multiplepilot tones, such as OFDM, including WLAN, 4G cellular, WiMax and UWB.Embodiments of the present invention may be applied to a varietypacket-based methods and standards. Thus, any packet-based method may bemodified such that it uses multiple pilot tones in the packet pre-ambleor packets that have room.

If the distance between the transmitter and receiver is smaller than athreshold (e.g., the speed of light divided by the frequency differenceof two tones), then the full cycle phase ambiguity issue disappears andthe problem simplifies such that it is possible to calculate the actualtransmitter-receiver separation distance from one transmitter. Thecalculated residual phase differences can then be plotted against thetone pair frequency differences and the fitted gradient of this lineused to calculate the separation distance. Each tone in an OFDM signalcan generate its own curve with a fitted gradient. The gradients canthen be combined to provide a better estimate for the separationdistance. The combination algorithm can be as simple as averaging ormore complex such as Kalman filtering. A single measured phasedifference can also be used to calculate the separation distance, albeitwith less accuracy. Multiple transmitters and triangulation can then beused to processes the range information and obtain the object'slocation.

Embodiments of the present invention are complementary to GPS since itworks in indoor locations, tunnels and urban canyon, where GPS signalsmay be weak.

The following detailed description and accompanying drawings provide abetter understanding of the nature and advantages of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system for determining the location of anelectronic device according to one embodiment of the present invention.

FIG. 2 illustrates the use of a pair of tones to determine a distancebetween electronic devices according to one embodiment of the presentinvention.

FIG. 3 illustrates differences between frequency tone pairs against themeasured phase differences.

FIG. 4A illustrates a system according to one embodiment of the presentinvention.

FIG. 4B illustrates a system according to one embodiment of the presentinvention.

FIG. 5 illustrates a method according to one embodiment of the presentinvention.

FIG. 6A-C illustrates a system according to one embodiment of thepresent invention.

FIG. 7 illustrates a range engine according to one embodiment of thepresent invention.

FIG. 8 illustrates determining the location of an electronic deviceaccording to one embodiment of the present invention.

DETAILED DESCRIPTION

Described herein are techniques for methods and systems for determiningthe location of a mobile device. In the following description, forpurposes of explanation, numerous examples and specific details are setforth in order to provide a thorough understanding of the presentinvention. It will be evident, however, to one skilled in the art thatthe present invention as defined by the claims may include some or allof the features in these examples alone or in combination with otherfeatures described below, and may further include modifications andequivalents of the features and concepts described herein.

Embodiments of the present invention may be used to determine a locationof an electronic device. Information regarding the distances betweenelectronic devices having known locations and electronic devices havingan unknown location may be used to determine the location (i.e.,position) of the electronic device at the unknown location. FIG. 1illustrates system 100 for determining the location of an electronicdevice according to one embodiment of the present invention. Electronicdevice 101 may reside in an unknown location, and it may be desirable todetermine the location of the device. Embodiments of the presentinvention may use signals transmitted between electronic device 101 andother electronic devices at known locations (e.g., electronic devices102-104) to determine the location of device 101. For example, in oneembodiment a signal that includes multiple frequency components may betransmitted between electronic device 101 at an unknown location andelectronic device 102 located at a known location A. The differentfrequency components, which differ in frequency by an amount Δf, willresult in a measurable phase difference, Δφ, at the receiving devicethat is related to the distance between the device transmitting thesignal and the device receiving the signal. Accordingly, by transmittingand receiving such a signal, the distance between each electronic devicewith a known location and the electronic device with the unknownlocation may be determined. For example, the signal that travels betweendevice 101 and device 102 has different frequency components Δf1 and acorresponding measurable phase difference Δφ1. Similarly, the signalthat travels between device 101 and device 103 has different frequencycomponents Δf2 and a corresponding measurable phase difference Δφ2.Likewise, the signal that travels between device 101 and device 104 hasdifferent frequency components Δf3 and a corresponding measurable phasedifference Δφ3. The known location of devices 2, 3 and 4, the measuredphase differences, and the frequency components can then be processed todetermine distances d1, d2, d3, and the location of device 101. Asdescribed below, it is to be understood that device 101 may send out onesignal, in which case Δf1=Δf2=Δf3.

In one embodiment, the electronic device 101 having the unknown locationreceives signals transmitted from electronic devices 102-104 todetermine the unknown location. In other embodiments, the electronicdevice 101 having the unknown location transmits one or more signals,which are received by electronic devices 102-104 to determine theunknown location. In other embodiments, the electronic device 101 havingthe unknown location transmits and receives signals, and electronicdevices 102-104 may transmit and receive signals. For example, some orall of the devices may both transmit and receive to improve the accuracyof the distance measurement. This provides more data to process and theaveraging that result from processing more information improves theaccuracy of the distance measurement since the effect of random errorsis reduced. In yet another embodiment the transmitter can transmit morethan once where each transmission has a different center frequency andthe receiver can receive and handle these different transmissions. Forexample, Wireless LAN 802.11a and 802.11b use two different frequenciesand if both the transmitter and receiver support 802.11a and 802.11bthen using both provides better averaging. Yet another embodiment is fora multi-radio transmitter to transmit more than once where eachtransmission uses a different radio that supports a different wirelessstandard, such as WLAN and UWB. If the receiver supports these differentwireless standards more data is gathered and location accuracy isimproved through averaging. Alternatively, the distances between one ormore devices having known locations (e.g., devices 102 and 103) and thedevice with the unknown location may be determined by transmittingsignals from devices with known locations to the device having theunknown location, and other distances between one or more devices havingknown locations (e.g., device 104) and the device with the unknownlocation may be determined by transmitting signals from the device withthe unknown location to the devices with known locations.

The locations of electronic devices 102-104 may be known by installingthe devices in fixed locations and storing the location information. The.location information is typically longitude, latitude and height (oraltitude). It may also be x, y and z co-ordinates relative to somereference point. Alternatively, electronic devices 102-104 may haveembedded GPS systems or GPS assist systems that may be used to determinethe precise location of these systems using GPS techniques. Threedevices with known locations may be used to determine the unknownlocation of a device in two dimensions (2D), and four devices with knownlocations may be used to determine the unknown location of a device inthree dimensions (3D).

FIG. 2 illustrates the use of a pair of tones to determine a distancebetween electronic devices according to one embodiment of the presentinvention. A transmitted signal includes two frequency components f₁ andf₂, which may differ in frequency by an amount Δf. The different signalfrequencies (or tones), f, will have different correspondingwavelengths, λ, that can be determined as follows:

λ=c/f,

where c is the speed of light (i.e., 3×10⁸ m/s). As illustrated in FIG.2, the transmitted signals will propagate between a device (atransmitter) at location A to another device (a receiver) located at B.The distance between the devices is the propagation distance d between Aand B.

The example shown in FIG. 2 illustrates that the two signals may beinitially in-phase (Δφ=0). However, other implementations may transmitsignals that are initially out of phase by some known amount. Thesignals propagate from the transmitter at location A to the receiver atlocation B, thereby traversing a distance d. When the signals arrive atlocation B, there is an accumulated phase difference, Δφ, which can bemeasured. If the signals are represented as sinusoids, a first pilottone f1 transmitted by the transmitter may be represented as:

y ₁ =A sin(w ₁ t+φ _(o)),

where w₁ is the frequency in radians and φ_(o) is the initial phaseoffset and may be zero. The received signal at location B is representedas:

y ₂ =B sin(w ₁ t+φ _(o)+φ₁),

where φ₁ is the total phase change across the distance, d, traveled. Thephase of y2 is related to distance as follows:

φ₁=2πd/λ ₁

where λ₁ is the wavelength of the tone with frequency f₁. Similarly, afrequency tone f₂ transmitted at location A is represented as:

y ₃ =C sin(w ₂ t+φ _(o)),

where w₂ is the frequency in radians and φ_(o) is the initial phaseoffset. The initial phase offset φ_(o) may be zero. The correspondingreceived tone at location B may be represented as:

y ₄ =D sin(w ₂ t+φ _(o)+φ₂),

where φ₂ is the total phase change across the distance, d, traveled forfrequency tone f₂. The phase of y₄ is related to distance as follows:

φ₂=2πd/λ ₂

where λ₂ is the wavelength of the signal with frequency f₂.

For both frequency tones, the distance, d, may be represented as aninteger number of full wavelengths and a fractional (or residual)wavelength. For example, φ₁ and φ₂ may be represented as follows:

$\phi_{1} = {{2\pi \; {d/\lambda_{1}}} = {{\frac{2\pi}{\lambda_{1}}\left( {{N_{1}\lambda_{1}} + {\frac{{\overset{\_}{\varphi}}_{1}}{2\pi}\lambda_{1}}} \right)} = {{2\pi \; N_{1}} + {\overset{\_}{\varphi}}_{1}}}}$$\phi_{2} = {{2\pi \; {d/\lambda_{2}}} = {{\frac{2\pi}{\lambda_{2}}\left( {{N_{2}\lambda_{2}} + {\frac{{\overset{\_}{\varphi}}_{2}}{2\pi}\lambda_{2}}} \right)} = {{2\pi \; N_{2}} + {\overset{\_}{\varphi}}_{2}}}}$

where λ₁ and λ₂ are the wavelengths of f₁ and f₂, N₁ and N₂ are integernumber of full cycles of f₁ and f₂ (i.e., integer number of wavelengthsof the signal corresponding to a distance), and φ₁ and φ₂ are theresidual non-integer phases of the frequency tones f₁ and f₂ acrossdistance, d. Accordingly, the total phase difference at location B is asfollows:

${{\Delta \; \varphi} = {{\varphi_{1} - \varphi_{2}} = {{\frac{2\pi \; d}{\lambda_{1}} - \frac{2\pi \; d}{\lambda_{2}}} = {{2{\pi \left( {N_{1} - N_{2}} \right)}} + \overset{\_}{\varphi_{1}} - \overset{\_}{\varphi_{2}}}}}},$

where (N₁−N₂) is the difference in the integer number of wavelengths ofthe two signals. If c is the speed of light, and f₁ and f₂ are the twofrequency tones then:

$\begin{matrix}{{\frac{2\pi \; d}{c}\left( {f_{1},f_{2}} \right)} = {{2\pi \; \left( {N_{1} - N_{2}} \right)} + \left( {\overset{\_}{\varphi_{1}} - \overset{\_}{\varphi_{2}}} \right)}} & {{Eqn}.\mspace{14mu} 1}\end{matrix}$

FIG. 3 illustrates differences between frequency tone pairs against themeasured phase differences. This figure illustrates that the phasedifference will accumulate up to 2π, and then begins increasing againfrom zero. If the distances are small such as:

$d \leq \frac{c}{\left( {f_{1} - f_{2\;}} \right)}$

one can then assume that N₁=N₂. In this case Eqn. 1 simplifies and it ispossible to calculate d from the residual phase differences. Supposethere are n tone frequencies in a signal transmission spectrum. Then foreach frequency there are n−1 cases where a residual phase difference canbe calculated. For example, for frequency f₁ the combinations are (f₁,f₀), (f₁, f₂), . . . , (f₁, f_(n-1)). The calculated residual phasedifference can be plotted against the pair frequency differences togenerate a straight line curve. The fitted gradient of this line canthen be used to calculate distance d.

The above formulation can also be generalized to the case whereinitially the two signals have a known fixed phase difference. Thisfixed offset will not however have any effect on the line's gradient.Similarly, any phase measurement calibration errors will shift the linebut will not affect its gradient. This is one of the advantages of adifferential phase system in that phase differences are relative ratherthan absolute values.

The horizontal axis of FIG. 3 measures frequency difference from a basefrequency. For a multi-frequency signal that has “n” frequency tones,FIG. 3 can be repeated for each of the “n” tones (f₀, f₁, . . . ,f_(n-1)), where each tone provides a gradient. The gradients can then becombined to provide a better estimate for a distance “d.” Thecombination algorithm may include averaging or a more complex algorithmsuch as Kalman filtering. The total number of frequency paircombinations where residual phase difference values can be calculated isas follows:

n(n−1)/2.

The division by 2 is necessary since there is no difference between (f₀,f₁) and (f₁, f₀). The distance, d, can be calculated from a single pairmeasurement, as was shown in the equations above. The averaging can beperformed by averaging gradients or simply using Eqn. 1 and averagingthe calculated values for d. Once the distance between a transmittingdevice and receiving device is calculated, the process can be repeatedwith other nearby devices, whereby the distance between each of theother devices may also be computed.

The short distance criterion

$d \leq \frac{c}{\left( {f_{1} - f_{2\;}} \right)}$

is an assumption. For example, if f=1 MHz and c=3×10⁸ m/s then as longas d is less or equal to 300 m N₁=N₂, then d can be calculated directlyfrom the residual phase difference calculations. If f=10 MHz then d hasto be less than or equal to 30 m for N₁ to be equal to N₂. For thegeneral problem, however, d is not assumed to be small. In this case,phase ambiguities N₁ and N₂ may be solved using integer ambiguitytechniques. This phase ambiguity means that an individual transmittercan only calculate the range subject to a possible ambiguity factor.However, this ambiguity may be resolved by using multiple transmittersat known locations.

Eqn. 1 considers one frequency pair measurement for a transmissionbetween two devices. However, it can be generalized for any pair offrequency measurements with any number of devices:

$\begin{matrix}{{\frac{2\pi \; d_{k}}{c}\Delta \; f_{ij}^{k}} = {{2\pi \; \Delta \; N_{ij}^{k}} + {\Delta \; \varphi_{ij}^{k}}}} & {{Eqn}.\mspace{14mu} 2}\end{matrix}$

Example devices may include a mobile device and an access point. In thiscase, d_(k) represents the distance from the mobile device to accesspoint k, Δf_(ij) ^(k) represents frequency difference between two tones(f_(i)−f_(j)) using access point k, ΔN_(ij) ^(k) represents thedifference between the number of full cycles associated with frequencytones f_(i) and f_(j) using access point k, and Δφ_(ij) ^(k) representsthe residual phase difference between frequency tones f_(i) and f_(j)using access point k.

In the case where there are three devices used to determine the locationof a device with unknown location, Eqn 2 gives:

$\begin{matrix}{{\frac{2\pi \; d_{1}}{c}\Delta \; f_{ij}^{1}} = {{2\pi \; \Delta \; N_{ij}^{1}} + {\Delta \; \varphi_{ij}^{1}}}} & {{Eqn}\mspace{14mu} 3} \\{{\frac{2\pi \; d_{2}}{c}\Delta \; f_{ij}^{2}} = {{2\pi \; \Delta \; N_{ij}^{2}} + {\Delta \; \varphi_{ij}^{2}}}} & {{Eqn}\mspace{14mu} 4} \\{{\frac{2\pi \; d_{3}}{c}\Delta \; f_{ij}^{3}} = {{2\pi \; \Delta \; N_{ij}^{3}} + {\Delta \; \varphi_{ij}^{3}}}} & {{Eqn}\mspace{14mu} 5}\end{matrix}$

From the above equations, it can be seen that the distances between thedevices with known locations and the device with unknown location d₁,d₂, and d₃ may be determined by solving the system of linear equations.For instance, the equations may be solved by measuring the phases φ ofeach tone, calculating Δφ for the different tones, calculating Δf fromthe known frequency values of the tones, and solving the system oflinear equations for d₁, d₂, and d₃ by selecting values of N by trialand error. The correct values of N will result in a solution for thesystem of equations and provide the distance results.

For an n tone signal there are n(n−1)/2 frequency pair combinationswhere residual phase difference values can be calculated. Thus, if thereare three access points then Eqns 3, 4 and 5 will result in 3n(n−1)/2equations which can be solved to find the location of the mobile device.For the general situation where there are p access points there will bep·n(n−1)/2 equations to solve for locating the mobile device. One methodto solve the equations is as follows. Given the access point locations,a positioning system may pick one access point and fix its ΔN_(ij) ^(k)to an integer and then try different integers for the other ΔN_(ij) ^(k)and for each integer combination try to solve the triangulation problemand see if a solution exists. For a two dimensional location problem,circles are drawn and they must intersect at one point for a validsolution. Three transmitters as access points may be used to solve thisproblem as mentioned above. For a three dimensional location problemspheres are drawn. Four transmitters may be used to solve this problemas mentioned above. This search process may continue until a validsolution is obtained. Other constraints may also be used during thissearch. For example, |d_(p)+d_(q)|>d_(pq), and |d_(p)−d_(q)|<d_(pq),where d_(pq) is the distance between the pth and qth access points and ∥is the modulus operator. This search process may be carried out by alocation engine which is running on a server. The physical location ofthe location engine may be embedded into a transmitting device, areceiving device, or an independent device such as a server. While thepresent description illustrates resolving the phase ambiguity usingexamples provided above, it is to be understood that other techniquesfor resolving the phase ambiguity may be used to determine the distancevalues.

In one embodiment, the solution to the above system of equations may beresolved by using amplitude information from the received tones toselect starting values of N. For example, in one embodiment theamplitudes of the received tones may be used to determine an estimate ofthe distance between a transmitting and receiving device. The estimatedrange may then be used to select values for N that are likely solutionsto the above equations. For example, in one embodiment, the amplitude ofthe received signal may be used to determine the received power. Thepower attenuation of a transmitted signal is related to range asfollows:

$P_{RX} \propto \frac{P_{TX}}{R^{2}}$

Where P_(RX) is the received power, P_(TX) is the transmitted power, andR is the distance. However, this distance measurement may not be veryaccurate. Nevertheless, if the received power is known (e.g., from theamplitude) and the transmitted power is known, then the distance may beestimated. The estimated distance may be used to determine values for Nin the equations above that will result in final distance results. Forexample, the estimated distance values may be used with the knownfrequency and phase differences to calculate estimated values for N,which may in turn be used to narrow the selection of values for N. Theselected values for N derived from the estimated values of the distancemay then be used to calculate final distance values. In one embodiment,the transmitted power may be stored as encoded data in the tones andsent from the transmitting device to the receiving device. In anotherembodiment, the transmitted power may be sent to a location engine andused as part of the location calculation process. It is to be understoodthe transmitted and received power of individual tones or the totalpower of transmitted and received signals may be used to determine theestimated distance.

FIG. 4A illustrates a system 400A according to one embodiment of thepresent invention. System 400A includes a first device 401 at knownlocation A, a second device 402 at known location B, a third device 403at known location C, a fourth device 404 at known location D, and adevice 405 at unknown location F. In this embodiment, devices 401-404may transmit signals and device 405 may receive the signals fordetermining the distance between each device having a known location andthe unknown location of device 405. In this example, each device 401-404transmits a signal 408-411 including a plurality of frequencies (tones):

(f ₀,φ₀),(f ₁,φ₁),(f ₂,φ₂), . . . ,(f _(n-1),φ_(n-1)).

The different signals 408-411 may include the same frequencies ordifferent frequencies as the other signals, or combinations thereof. Forexample, signal 408 and signal 409 may contain the same frequencies,while signal 409 and signal 410 may share only some of the samefrequencies, but otherwise use different frequencies. As described inmore detail below, different multi-frequency protocols may be usedbetween different devices to determine the distance.

Device 405 receives the signals 408-411 from the devices 401-404. Thesignals from each device 401-404 will be received with some detectablephase change. The distance may be determined by processing the receivedsignals. For example, in one embodiment the received signals may beconverted from analog signals into digital signals and processed usingdigital signal processing. Processing may include determining the phaseof the received frequency components, determining the frequencycharacteristics of the transmission channel, and determining the phasedifferences. Processing may further include calculating distances usingthe phase difference results and determining the location of theelectronic device 405 by identifying a point on a plurality of circles(or spheres) of radius, d_(i), where d_(i) is the distance from a devicehaving a known location to the device of unknown location, where allfour circles (or spheres) intersect. The 2D locating problem requires aminimum of three circles intersecting in one point in 2D. The 3D problemrequires a minimum of four spheres intersecting at one point in 3D. Asillustrated in FIG. 4A, processing the signal information may beperformed (in whole or in part) by a location engine. In the exampleillustrated in FIG. 4A, the signal information may be sent fromelectronic device 405 through any one of the other electronic devices(e.g., device 404) and network 450 to a server 407. Network 450 may be awired and wireless network (e.g., a LAN or WAN) and may include theInternet, for example. Server 407 includes a location engine 451 fordetermining the location of electronic device 405. The location enginemay receive either the raw data for the digitized signals orpreprocessed data, such as extracted phase differences and estimatedfrequency responses, for example, for determining the location of thedevice. In other embodiments, the location engine may be included on oneof the electronic devices 401-404 as illustrated at 451A. In yet otherembodiments, the location engine may be included as part of electronicdevice 405 as illustrated at 451B. As described in more detail below,the location engine may include multiple components for performingdifferent processing tasks such as phase extraction and channelestimation for each of the individual transmissions between the device405 and the other devices 401-404 or determining the final location ofdevice 405, for example. In some embodiments, the location enginecomponents may be implemented on different devices in the system. In oneexample application, location engine 451 on server 407 may calculate thelocation and return this information back to the device 405. In oneembodiment, embedded navigation software may help a user of device 405navigate to a desired location (e.g., if device 405 is a cell phone ormobile wireless device). In another embodiment, device 405 may have agyrator that can provide a differential vector of movement relative toprevious positions. This can be used to minimize the errors of thesystem. For example, if there are system errors and the final calculatedposition of device 405 fluctuates widely from before then the relativemovement vector of the gyrator may be used to reduce errors by addingthe movement vector to a previous more reliable calculated position orby combining the latest calculated position with the gyrator movementvector.

FIG. 4B illustrates a system 400B according to one embodiment of thepresent invention. In this example system, device 405 may transmitsignals and devices 401-404 may receive the signals for determining thedistance between each device having a known location and the unknownlocation of device 405. Similar to the example in FIG. 4A, the differentsignals 418-421 may include the same frequencies or differentfrequencies, or combinations thereof. Devices 401-404 receive thesignals 418-421 from device 405. The signals will be received with somedetectable phase change. The distance may be determined by processingthe received signals as described above. In this example, the signalinformation is initially in each device 401-404. This information may besent from a device where the signal is received to a server 407, to anyone of the other electronic devices receiving a signal, or even back tothe transmitting device for processing by a location engine or componentthereof.

FIG. 5 illustrates a method 500 according to one embodiment of thepresent invention. At 501, a first signal having a plurality offrequency components (tones) is transmitted between a first device at anunknown location and a device at a known location. At 502, a secondsignal having a plurality of frequency components is transmitted betweenthe first device at the unknown location and another device at anotherknown location. At 503, a third signal having a plurality of frequencycomponents is transmitted between the first device at the unknownlocation and yet another device at another known location. This processmay be repeated for any number of devices within range of the device atthe unknown location. Four devices at known locations are sufficient fordetermining the location of the unknown device in 3D. At 504, the phasedifferences with corresponding frequency differences are determined foreach transmission between a device at a known location and the device atthe unknown location. At 505, the location of the first device isdetermined from the phase and frequency differences. For example, thesystem may determine where circles or spheres intersect in one point tolocate the device. Additionally, the system can calculate the distancesbetween the devices.

Embodiments of the present invention may locate different electronicdevices using a variety of different multi-frequency transmissiontechnologies. Example electronic devices that may be located includemobile electronic devices such as cellular phones, personal digitalassistants (PDA), laptop computers, or any other electronic device withfunctionality to send or receive signals as described herein. Exampleelectronic devices having known locations may include wireless networkaccess points (e.g., an 802.11 access point) or base station (e.g., acellular base station), for example. In another embodiment described inmore detail below, the position of a first electronic device with aninitially unknown location may be determined using multiple otherdevices with known locations, and the position of another device with anunknown location may be determined using the discovered position of thefirst device. This ad-hoc network positioning system is described inmore detail below.

Example Implementation

In one exemplary implementation, embodiments of the present inventionmay transmit orthogonal frequency division multiplexing signals betweendevices to determine the distance. Orthogonal frequency divisionmultiplexing (OFDM) is a communications technique that divides acommunications channel into a number of frequency bands. OFDM is alsoreferred to as multi-tone modulation. FIG. 6A illustrates an example ofan OFDM signal having a plurality of frequencies that may be transmittedbetween a device having a known location and a device having an unknownlocation to determine position. This example OFDM signal includes acarrier frequency (or center frequency) and a plurality of sub-carriershaving different frequencies. The sub-carriers are typically spreadsymmetrically around the carrier frequency. The frequency bands areequally spaced at a distance, in frequency, of 1/Ts, where Ts is thetime period corresponding to the frequency spacing. Typically, eachsub-carrier frequency is used to encode a portion of the informationtransmitted, and each sub-carrier frequency resides within a frequencyband. All the sub-carrier frequencies are combined and transmittedsimultaneously for a certain time period. The time period oftransmission of a certain data set encoded in the sub-carriers acrossall the frequencies (and modulated at the carrier frequency) is called asymbol period, and the transmitted tones for that period is a symbol. Inan exemplary OFDM system, each sub-carrier is orthogonal (independent ofeach other) with every other sub-carrier, differentiating OFDM from thefrequency division multiplexing (FDM). Therefore, these OFDM systemsallow the spectrum of each tone to overlap because the tones areorthogonal and do not interfere with each other. The overall amount ofspectrum that is required is reduced because the tones overlap.

Exemplary OFDM systems spread the data to be transmitted over a largenumbers of carriers, each of which is modulated at a low rate. The tonesin these OFDM systems have the very special property of being the onlyEigen-functions of a linear channel. This prevents interference betweenadjacent tones in OFDM systems. The baseband OFDM signals in a systemwith n frequency tones can be written as:

${{x(t)} = {\sum\limits_{m = 0}^{n - 1}{X_{m}{\exp \left( {j\; 2\pi \frac{m}{T}t} \right)}}}},{0 \leq t \leq T}$Where: $f_{m} = \frac{m}{T}$

is the central frequency of the mth sub-channel and X_(m) is thecorresponding transmitted symbol.The signals:

$\exp \left( {j\; 2\pi \frac{m}{T}t} \right)$

are orthogonal over [0, T] as illustrated below:

${{1/T}{\int_{0}^{T}{{{\exp \left( {j\; 2\pi \frac{m}{T}t} \right)} \cdot {\exp \left( {{- 2}\; j\ \pi \frac{l}{T}t} \right)}}{t}}}} = \delta_{ml}$

The frequency domain representation of a number of tones demonstratesthat the peak of each tone corresponds to a zero level, or null, ofevery other tone. The result of this is that there is no interferencebetween tones. When the receiver samples at the center frequency of eachtone, the only energy present is that of the desired signal, pluswhatever other noise happens to be in the channel.

Individual sub-channels can be completely separated by a receiver's FastFourier Transform (FFT) if there are no Inter-Symbol Interference (ISI)and Inter-Carrier Interference (ICI) introduced by the channel.Multi-path propagation can cause linear distortions, spread energy intoadjacent channels, and cause ISI and ICI. Some implementations of OFDMsystems are more robust to multi-path effects and prevent ISI and ICI bycreating a cyclically extended guard interval called a cyclic prefix,where each OFDM symbol is preceded by a periodic extension of thesignal. ISI and ICI can be eliminated when the guard interval is longerthan the channel impulse response or multi-path delay. The overheadintroduced by the cyclic prefix, however, increases with the length ofthe cyclic prefix. Some OFDM systems also reduce frequency selectivefading by averaging over all frequencies.

Some embodiments of the present invention may determine the location ofa mobile electronic device using several access points (orbase-stations) with known coordinates. The resolution of the location ofa mobile device may include the case where the accesspoints/base-stations are OFDM transmitters and the mobile device is thereceiver, or the case where the mobile device is the OFDM transmitterand the access points/base-stations are the receivers, or yet othersituations where some access points/base-stations are OFDM transmittersand some are receivers. The proposed method can be applied to any systemthat is based on any OFDM scheme or uses multiple pilot tones including,but not limited to, 802.11, WLAN, 4G cellular, WiMax, and UWB standard.Other systems such as Bluetooth may also be used where one transmittedpacket contains multiple frequency tones that are used for positioningas described herein. The proposed methodology may be used where thetransmitter and receiver use the same standard and protocol, but not allaccess points/base stations used to determine the location of the mobiledevice need to use the same standard and protocol.

The accuracy of the location measurement improves as more transmissionswith devices having known locations are utilized and as more frequencypair combinations are used for each transaction. The accuracy of thesystem can also be increased by increasing the number of OFDM frequencytones and increasing the bandwidth and frequency distance between thetones. These factors average out and reduce the effects of fading andmultipath. The Media Access Control (MAC) layer typically determines thenumber of tones. Also, in Multiple-Input and Multiple-Output (MIMO)systems it is possible to use several antennas to gather more data anddo more averaging to get more accurate results. For example, a MIMOaccess point acting as a transmitter can use more than one antenna. In aspecific example, an access point can have 4 or more antennas. So inFIG. 4A the four transmitters are from one physical access point. Buteach transmitter represents one of the antenna of the multiple antennaaccess point. Likewise, in FIG. 4B the receivers can each be one of theantenna of a multiple antenna access point. If the location of each ofthe antenna of the access point that are used is known thentriangulation can be used for locating the mobile device. Hybrid casesare also possible where for example in FIG. 4A some of the transmittersare from different antenna on the same physical multiple antenna accesspoint and other transmitters are from physically different accesspoints. Likewise, in FIG. 4B some of the receivers may be differentantenna of the same physical multiple antenna access point and otherreceivers are physically different access points. A mobile device canalso have multiple antenna so it can transmit using each antenna orreceive with each antenna.

Furthermore, it is possible to use just those antennas with the highestperformance, lowest bit error rates, and better line of sight. In ultrawideband (UWB) systems, a plurality of tones may be transmitted andreceived simultaneously as well. As mentioned above, in one embodimentthe access points/base-stations are transmitters and mobile device isthe receiver. In another embodiment the access points/base-stations arereceivers and the mobile device is the transmitter. In anotherembodiment, the access points/base-stations and mobile device aretransmitters and receiver. This may be advantageous in systems wheretransmit and receive frequencies are different. For example, somecellular systems transmit at 1 GHz and receive at 1.1 GHz. Switching therole of transmitter and receiver therefore provides more data samplesand equations to solve. Also some systems such as wireless local areanetwork (WLAN) can operate at different frequencies. For example, WLAN802.11a and 802.11g use two different frequencies and using bothfrequencies provides more data for processing and getting a moreaccurate location. Another way to improve location accuracy is to useseveral wireless standards. For example, if an access point and a mobiledevice both have UWB and WLAN connectivity then data may be obtainedfrom both standards and processed to get a more accurate location value.

After the mobile device's position is calculated, it is possible tointerface the system with a navigation system that provides pathplanning and guidance. In another configuration a mobile device whoseposition is known or calculated can also be used as an access point tolocate the position of other mobile devices.

FIG. 6B illustrates another example method of determining the locationof a mobile device according to another embodiment of the presentinvention. At 650, a number “n” representing the number of transmittershaving known locations is initialized (n=1). At 651, the firsttransmitter transmits multiple pilot tones (e.g., OFDM tones). At 652,the receiver (e.g., a mobile device) receives the signal and extractsthe pilot tones. At 653, the receiver sends the pilot tone pair phasedifferences, which may include a plurality of phase difference valuescorresponding to the phase difference between some or all of the tones,to a server. The amplitudes of the different received tones may also besent to the server. Additionally, the coordinates of the transmitter maybe sent to the server. At 654, the number “n” is incremented, indicatingthat the next transmitter should transmit. At 655, the number “n” iscompared to the number of transmitters. If all the transmitters have nottransmitted, then the process returns to step 651, and the nexttransmitter sends a signal and steps 652 through 654 are repeated. Ifall the transmitters have transmitted (n>number of transmitters), thenthe server processes the phase difference data, tone amplitudes, andcoordinates of transmitters to determine the location of the receiver at656.

FIG. 6C illustrates a system 600 according to one embodiment of thepresent invention. The transmitter 601 is a OFDM transmitter. Althougheach standard (WLAN, WiMax, Cellular, etc.) may have slightly differentimplementation than this figure, the techniques for determining thelocation of an unknown device as applied to system 600 may be appliedother standards. The receiver 603 is also a OFDM receiver including anOFDM range engine block 623 and location engine 624. The transmitter 601receives input bits representing data such as voice, text or other kindsof information and performs channel coding 602. Channel coding protectsdata sent over the communication channel in the presence of noise.Channel coding is usually performed with forward error correction, whereredundant bits are added to the information bits. These added bits thenallow the receiver to detect and correct small errors without asking fortransmission of additional data from the transmitter. Interleaving 603may be part of the channel encoder 602 and may be used to randomizeerrors by exploiting frequency diversity and providing robustnessagainst multi-path and interference. Each sub-carrier may be modulated604 with a conventional modulation scheme (e.g. PSK/QAM). The data maybe transformed from a serial representation to a parallel representationat 605. The pilot insertion block 606 inserts the pilot tones. Theamplitude and phase of these pilot tones are stored and used forestimating channel attenuation and channel equalization. After the datamodulation step these pilot tones become the subcarriers. The details ofthe implementation vary depending on the standard (e.g. WLAN, WiMax,Cellular). Some standards may use different frequencies at the same timewhile others may use the same frequency at different times. After theinsertion step an n-point inverse fast Fourier transform (IFFT) 607 maytransform the data sequence. The guard insertion block 608 may insert acyclic extension of a time length that is larger than the expected delayspread to avoid inter-symbol and inter-carrier interference. The data isconverted from a parallel representation to a serial representation 609.The Digital-to-Analog (D/A) converter 610 changes the signal into theanalog domain and contains Low-Pass Filters (LPF) that match thesampling interval. After conversion, the signal is modulated at 651 by acarrier wave having a carrier frequency and transmitted. This step isalso referred to as “up conversion” because the signals having aplurality of frequencies are being moved in frequency up to a higherfrequency that is typically symmetric around the carrier frequency.

The wireless channel 611 in FIG. 6 is modeled as an impulse response “h”followed by complex Additive White Gaussian Noise (AWGN) 612. Thereceiver 614 performs demodulation of the modulated signal at 652 andAnalog-to-Digital (A/D) conversion and low-pass filtering at 614. Thedemodulation step at 652 is also referred to as “down conversion”because the signals having a plurality of frequencies are being moved infrequency back down from the carrier frequency to their originalfrequencies. The data may then go through serial to parallel conversion615 and guard removal 616. A fast Fourier transform (FFT) block 617transforms the data back into the original form. The signals areextracted and channel estimation is performed 618. The signals andestimated channel information are then used by the OFDM range engine 623to calculate the residual phase differences between two frequency tonesand extract amplitude information for each tone. The data is convertedfrom a parallel to a serial representation 619. The binary informationis obtained after demodulation 620 that demodulates the frequencysub-carriers, de-interleaving 621, and channel decoding 622. Blocks 651and 652 perform carrier frequency up/down conversion, whereas 604 and620 carry out sub-carrier modulation and demodulation.

The receiver 613, optionally, has a location engine 624. This locationengine 624 may be used in instances where the receiver 613 is used forlocation calculation via methods such as triangulation search methods.Thus, the location engine uses its calculated residual phase differencesand tone amplitude information for each of the access points tocalculate its own position. If the receiver 613 does not have a locationengine 624 to calculate its own position it can transmit the calculatedresidual phase differences and tone amplitude information to a networkserver or another mobile device for location calculations.

Time and the index representing the access point are not shown in theequations below to avoid repetition. For example, Eqn 2 used index k torefer to a specific access point. A time index also means representing areceived signal Y as Y(t) where t represents a particular time instance.Suppose that the received signal by the receiver in FIG. 6 isrepresented by Y. Then Y can be represented as:

Y=X·H+W

Where:

Y=[y ₀ ,y ₁ , . . . ,y _(n-1)]

is the received OFDM symbol vector and:

X=[x ₀ ,x ₁ , . . . ,x _(n-1)]

is the transmitted OFDM symbol vector and:

H=[h ₀ e ^(jφ) ⁰ ,h ₁ e ^(jφ) ¹ , . . . ,h _(n-1) e ^(jφ) ^(n-1) ]

is the frequency response vector of the channel and:

W=[w ₀ ,w ₁ , . . . ,w _(n-1)]

is the Additive White Gaussian Noise (AWGN) vector. FIG. 7 illustrates arange engine 700 according to one embodiment of the present invention.Channel estimation algorithms in OFDM provide estimates for H. The OFDMrange engine 700 then uses the estimated channel frequency responsevector 701 to extract phase information at 703 to calculate the residualphase differences, Δφ_(ij) ^(k), of Eqn. 2 and extract amplitudeinformation at 702 for each tone. The Δf_(ij) ^(k) tone frequencydifferences of Eqn. 2 can be calculated based on the spacing betweenOFDM tone subcarriers. The amplitude information may also be used toestimate range between devices as describe above, for example, where therange may be estimated by correlating the transmitted power and thereceived signal amplitude with the distance traveled. Additionally, inone embodiment the tone amplitude information may be used to reduce theeffects of noise, fading or multipath. For example, the impact of suchadverse channel effects may be reduced by weighting the tones based onreceived amplitudes, which may be normalized, for example. In oneembodiment, the amplitudes of the received tones may be averaged, andweights may be assigned to each tone based on the amplitude of each tonerelative to the average amplitude. In another embodiment, the highestand lowest received tone amplitudes are determined, and weights areassigned to each tone based on the amplitude of the tone relative to therange of received amplitudes. Accordingly, smaller received amplitudesmay be given smaller weights in the location calculations or ignoredaltogether because it could represent noise or fading Amplitudeinformation may also be used to detect multi-paths. For example, thevariation in amplitude across all the received tones may be determinedAccess points that provide a direct line of sight will have fewervariations in the amplitudes of their tones and will be preferred in thetriangulation calculations in order to reduce the effects of multipath.

The example embodiment shown in FIG. 7 uses OFDM. Other packet-basedmethods and standards may be utilized as well. Many packet-based methodsmay be modified such that it uses n pilot tones in the packet pre-ambleor packets that have room. In one embodiment the transmitters may benearby WLAN or 4G cellular or WiMax or UWB access points/base-stations,and the mobile device is a portable electronic device such as a cellularphone, personal digital assistant (“PDA”), or watch, or any computerbased system, for example.

FIG. 8 illustrates determining the location of an electronic deviceaccording to one embodiment of the present invention. FIG. 8 illustratesthat the distance between one device 801 having an unknown location maybe used to determine the location of another device 806 having anunknown location if the first device is within range of devices withknown locations or if the device has a GPS technology. For example,tones having different frequencies may be transmitted between devices802, 803, 804, and 805 and device 801, resulting in corresponding phasedifferences that may be used to determine the distances between thedevices at known locations and device 801. Accordingly, the location ofdevice 801 may be determined Additionally, tones having differentfrequencies may be transmitted between device 801 and device 806,resulting in corresponding phase differences. In one embodiment, ifthree other devices having known locations are within range (e.g.,devices 802, 803, and 804 are in range, but device 805 is not in range),the location of device 806 may be determined using tones from each ofthese devices and tones from device 801. As a specific example, devices801 and 806 may be mobile devices and devices 802-805 may be wirelessaccess points. The location of mobile device 806 may be determined usinga combination of signals from one or more access points and one or moreother mobile devices that have known locations based on other accesspoints. In one embodiment, if a mobile device having an unknown locationis out of range of all access points having known locations, thelocation of the mobile device may still be determined if the mobiledevice is within range of other mobile devices that are within range ofaccess points with known locations. Similarly, if a mobile device havingan unknown location is out of range of all access points having knownlocations, the location of the mobile device may still be determined ifthe mobile device is within range of other mobile devices with knownlocations obtained through GPS. In that example, one or more mobiledevices may have known locations using GPS technology (or positionassisted GPS), and the location of another mobile device that does nothave GPS may be determined using the techniques described above.

The above description illustrates various embodiments of the presentinvention along with examples of how aspects of the present inventionmay be implemented. The above examples and embodiments should not bedeemed to be the only embodiments, and are presented to illustrate theflexibility and advantages of the present invention as defined by thefollowing claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentswill be evident to those skilled in the art and may be employed withoutdeparting from the spirit and scope of the invention as defined by theclaims.

1-22. (canceled)
 23. A system for determining a location of anelectronic device, the system comprising: (i) a first electronic devicecomprising: (a) a plurality of antennas located at known locations, theplurality of antennas comprising three or more antennas; and (b) areceiver; (ii) a second electronic device located at an unknownlocation, the second electronic device comprising: (a) an antenna; and(b) a transmitter; and (iii) a location determination engine, whereinthe transmitter of the second electronic device is configured totransmit one or more signals from the antenna of the second electronicdevice to the first electronic device located at the known location,each transmitted signal including a plurality of simultaneous pilottones having different frequencies; wherein the receiver of the firstelectronic device is configured to: (a) determine a first accumulatedphase difference between at least two pilot tones having a firstfrequency difference in a signal transmitted from the antenna of thesecond electronic device and received at a first antenna of the firstelectronic device; (b) determine a second accumulated phase differencebetween at least two pilot tones having a second frequency difference ina signal transmitted from the antenna of the second electronic deviceand received at a second antenna of the first electronic device; (c)determine a third accumulated phase difference between at least twopilot tones having a third frequency difference in a signal transmittedfrom the antenna of the second electronic device and received at a thirdantenna of the first electronic device; and wherein the locationdetermination engine is configured to determine the location of thesecond electronic device using said first, second, and third accumulatedphase differences and said first, second, and third frequencydifferences.
 24. The system of claim 23, wherein the first electronicdevice comprises said location determination engine.
 25. The system ofclaim 23 further comprising a server comprising said locationdetermination engine, wherein the first electronic device is configuredto send said first, second, and third phase differences and said first,second, and third frequency differences to the server through a network.26. The system of claim 23, wherein the second electronic devicecomprises said location determination engine, wherein the firstelectronic device is configured to send said first, second, and thirdphase differences and said first, second, and third frequencydifferences to the second electronic device.
 27. The system of claim 23,wherein the transmitter of the second electronic device comprises apilot insertion component configured to insert said pilot tones into thesignals transmitted from the transmitter of the second electronicdevice.
 28. The system of claim 23, wherein the transmitter of thesecond electronic device is further configured to transmit said signalsthrough a transmission channel, wherein the receiver of the firstelectronic device comprises: a pilot extraction and channel estimationcomponent configured to (i) extract said pilot tones from signalsreceived at the plurality of the antennas of the first electronic deviceand (ii) estimate a frequency response vector for the transmissionchannel using the extracted pilot tones; and a range engine configuredto calculate said phase differences accumulated between said pilot tonesusing the estimated frequency response vector.
 29. The system of claim28, wherein the range engine is further configured to: extractamplitudes of each received pilot tone, use the amplitudes of each ofthe pilot tones of the one or more signals to determine a receivedpower, and use an attenuation in the received power to determinedistances between the second electronic device and the first, second,and third antennas of the first electronic device.
 30. The system ofclaim 29, wherein the location determination engine is furtherconfigured to determine the location of the second electronic device byusing the determined distances to triangulate the location of the secondelectronic device.
 31. The system of claim 29, wherein the range engineis further configured to assign weights to each pilot tone of thesignals based on the amplitude of each pilot tone relative to an averageamplitude in order to reduce the effects of noise, fading, or multipath.32. The system of claim 23 further comprising: a third electronic devicecomprising an antenna at a known location, wherein the third electronicdevice is configured to transmit one or more signals each including aplurality of pilot tones having different frequencies from the antennaof the third electronic device to the plurality of antennas of the firstelectronic device, wherein the receiver of the first electronic deviceis further configured to determine a fourth accumulated phase differencebetween at least two pilot tones having a fourth frequency difference ina signal transmitted from the antenna of the third electronic device andreceived at an antenna of the first electronic device, wherein thelocation determination engine is further configured to use the fourthaccumulated phase difference and the fourth frequency difference todetermine the location of the second electronic device.
 33. The systemof claim 23, wherein the plurality of antennas of the first electronicdevice comprise a fourth antenna at a known location, wherein thereceiver of the first electronic device is further configured todetermine a fourth accumulated phase difference between at least twopilot tones having a fourth frequency difference in a signal transmittedfrom the antenna of the second electronic device and received at thefourth antenna of the first electronic device, wherein said determiningthe location by the location determination engine further comprisesusing the fourth accumulated phase difference and the fourth frequencydifference.
 34. The system of claim 23, wherein the first electronicdevice is an access point, wherein the second electronic device is amobile device, wherein the plurality of antennas are antennas at knownlocations of the access point.
 35. The system of claim 23, wherein thelocation determination engine is further configured to determine thelocation of the second electronic device based on distances between thesecond electronic device and the first, second, and third antennas ofthe first electronic device, each of the distances determined by solvinga system of linear equations based on the accumulated phase differences,wherein the system of linear equations is solved by trial and error byinputting integer numbers representing full cycles for each pilot tone.36. The system of claim 23, wherein the first electronic device and thesecond electronic device utilize a plurality of wireless standardscomprising Ultra-Wideband and Wireless Local Area Network.
 37. Thesystem of claim 23, wherein the plurality of pilot tones included in thesignals transmitted from the antenna of the second electronic device andreceived at the plurality of antennas of the first electronic devicehave a known phase difference at a time of transmission, wherein thelocation of the second electronic device is determined based ondistances between the second electronic device and the first, second,and third antennas of the first electronic device, each of the distancesdetermined based on the determined accumulated phase differences and theknown phase difference.
 38. The system of claim 23 further comprising anavigation system, wherein the second electronic device is configured tointerface with the navigation system to provide path planning andguidance when the location of the second electronic device isdetermined.
 39. The system of claim 23 further comprising a plurality ofmobile devices, wherein the second electronic device is configured tofunction as an access point of a known location to locate positions ofone or more mobile devices in the plurality of mobile devices when thelocation of the second electronic device is determined.
 40. The systemof claim 23, wherein the signals transmitted from the antenna of thesecond electronic device to the plurality of antennas of the firstelectronic device comprise orthogonal frequency division multiplexed(OFDM) signals.
 41. The system of claim 23, wherein the transmitter ofthe second electronic device is further configured to transmitpacket-based signals from the antenna of the second electronic device tothe plurality of antennas of the first electronic device, wherein thepacket-based signals include said pilot tones in a packet preamble. 42.The system of claim 23, wherein the transmitter of the second electronicdevice is further configured to transmit packet-based signals from theantenna of the second electronic device to the plurality of antennas ofthe first electronic device, wherein the packet-based signals include aset of packets that include said pilot tones.
 43. A first electronicdevice, comprising: a plurality of antennas located at known locations,the plurality of antennas comprising three or more antennas; and areceiver, the receiver configured to: receive one or more signalstransmitted from a second electronic device located at an unknownlocation, each received signal including a plurality of simultaneouspilot tones having different frequencies; determine a first accumulatedphase difference between at least two pilot tones having a firstfrequency difference in a signal transmitted from the second electronicdevice and received at a first antenna of the first electronic device;determine a second accumulated phase difference between at least twopilot tones having a second frequency difference in a signal transmittedfrom the second electronic device and received at a second antenna ofthe first electronic device; determine a third accumulated phasedifference between at least two pilot tones having a third frequencydifference in a signal transmitted from the second electronic device andreceived at a third antenna of the first electronic device; and whereinthe first electronic device is configured to determine a location of thesecond electronic device using said first, second, and third accumulatedphase differences and said first, second, and third frequencydifferences.
 44. The electronic device of claim 43, wherein the receiverof the first electronic device is further configured to receive saidsignals through a transmission channel, wherein the receiver of thefirst electronic device comprises: a pilot extraction and channelestimation component configured to (i) extract said pilot tones fromsignals received at the plurality of the antennas of the firstelectronic device and (ii) estimate a frequency response vector for thetransmission channel using the extracted pilot tones; and a range engineconfigured to calculate said phase differences accumulated between saidpilot tones using the estimated frequency response vector.
 45. Theelectronic device of claim 44, wherein the range engine is furtherconfigured to: extract amplitudes of each received pilot tone, use theamplitudes of each of the pilot tones of the one or more signals todetermine a received power, and use an attenuation in the received powerto determine distances between the second electronic device and thefirst, second, and third antennas of the first electronic device. 46.The electronic device of claim 45, wherein the first electronic deviceis further configured to determine the location of the second electronicdevice by using the determined distances to triangulate the location ofthe second electronic device.
 47. The electronic device of claim 45,wherein the range engine is further configured to assign weights to eachpilot tone of the signals based on the amplitude of each pilot tonerelative to an average amplitude in order to reduce the effects ofnoise, fading, or multipath.
 48. The electronic device of claim 43,wherein the plurality of antennas of the first electronic devicecomprise a fourth antenna at a known location, wherein the receiver ofthe first electronic device is further configured to determine a fourthaccumulated phase difference between at least two pilot tones having afourth frequency difference in a signal transmitted from the secondelectronic device and received at the fourth antenna of the firstelectronic device, wherein said determining the location furthercomprises using the fourth accumulated phase difference and the fourthfrequency difference.
 49. The electronic device of claim 43, wherein thereceiver of the first electronic device is further configured to:receive one or more signals each including a plurality of pilot toneshaving different frequencies from an antenna of a third electronicdevice at a known location; and determine a fourth accumulated phasedifference between at least two pilot tones having a fourth frequencydifference in a signal transmitted from the antenna of the thirdelectronic device at a known location and received at an antenna of thefirst electronic device, wherein the first electronic device is furtherconfigured to use the fourth accumulated phase difference and the fourthfrequency difference to determine the location of the second electronicdevice.
 50. The electronic device of claim 43, wherein the firstelectronic device is an access point, wherein the second electronicdevice is a mobile device, wherein the plurality of antennas areantennas at known locations of the access point.
 51. The electronicdevice of claim 43, wherein the first electronic device is furtherconfigured to determine the location of the second electronic devicebased on distances between the second electronic device and the first,second, and third antennas of the first electronic device, each of thedistances determined by solving a system of linear equations based onthe accumulated phase differences, wherein the system of linearequations is solved by trial and error by inputting integer numbersrepresenting full cycles for each pilot tone.
 52. The electronic deviceof claim 43, wherein the first electronic device and the secondelectronic device utilize a plurality of wireless standards comprisingUltra-Wideband and Wireless Local Area Network.
 53. The electronicdevice of claim 43, wherein the plurality of pilot tones included in thesignals received at the plurality of antennas of the first electronicdevice from the second electronic device have a known phase differenceat a time of transmission, wherein the location of the second electronicdevice is determined based on distances between the second electronicdevice and the first, second, and third antennas of the first electronicdevice, each of the distances determined based on the determinedaccumulated phase differences and the known phase difference.
 54. Theelectronic device of claim 43, wherein the signals received at theplurality of antennas of the first electronic device from the secondelectronic device comprise orthogonal frequency division multiplexed(OFDM) signals.
 55. The electronic device of claim 43, wherein thereceiver of the first electronic device is further configured to receivepacket-based signals from the second electronic device, wherein thepacket-based signals include a plurality of pilot tones in a packetpreamble.
 56. The electronic device of claim 43, wherein the receiver ofthe first electronic device is further configured to receivepacket-based signals from the second electronic device, wherein thepacket-based signals include a set of packets that include a pluralityof pilot tones.